1. Field of the Invention
The present invention relates generally to escape devices used to lower an endangered person from an elevated structure along an escape cable in the event of an emergency, and more particularly, to such an escape device incorporating an automatic brake which permits the endangered person to initially descend rapidly to escape the site of the emergency, while automatically slowing the rate of descent as the endangered person approaches the lower end of the escape cable.
2. Description of the Prior Art
When drilling wells and installing tubing within such wells, it is often necessary to station workers at one or more elevated stations within a derrick to perform certain various operations. In the event of a fire or other emergency, it is necessary to quickly evacuate such workers from the derrick.
Various types of escape devices adapted to lower endangered workers from elevated stations of a derrick, tower, or other elevated structure, are known in the art. One relatively simple escape device is sold under the trademark "GERONIMO" by Taber Welding Company of Perry, Okla., and consists of an L-shaped bar suspended from a box housing a pair of pulleys and equipped with a manual brake lever. The pulleys engage an escape cable extending between the elevated structure and a ground-based anchor. A person using this escape device seats himself upon the lower portion of the L-shaped bar while grabbing the upper portion of the bar with one hand and regulating his descent along the escape cable by operating the manual brake lever with his other hand. While generally serving its intended purpose, the "GERONIMO" escape device requires the endangered person to use both of his hands in order to safely descend from the elevated structure. Yet, following the occurrence of a fire or other emergency, workers stationed atop the elevated structure may sustain injuries which prevent such workers from using both of their hands to operate such an escape device.
U.S. Pat. No. 3,826,335 issued to Allen describes an apparatus for moving persons from atop a drilling rig or the like to the ground wherein a gondola is supported from an escape cable, and an automatic brake controls the descent of the gondola. A brake cable is coupled at one end to the gondola and is engaged about a set of sheaves associated with a counter weight that moves vertically upon rollers engaged within a vertical track. Vertical movement of the counter weight, and hence movement of the brake cable and gondola, is controlled by a hydraulic piston and cylinder and by an adjustable orifice. A manual brake is also incorporated into the gondola. However, the descent of the gondola along the escape cable is believed to be essentially linear. Moreover, the counterweight, sheaves, piston and cylinder, and other components of the braking system are relatively bulky, expensive, and somewhat difficult to install upon the derrick or other elevated structure. Further, the apparatus described by Allen is limited to use with a single elevated station, whereas the derrick or other elevated structure may include more than one elevated station from which a worker must be able to escape.
U.S. Pat. No. 4,056,167 issued to Bonafos discloses an emergency elevator for automatically controlling the descent of an endangered person from a derrick or other elevated structure. The emergency elevator includes a chamber suspended from a supporting cable for transporting an endangered person downwardly along the supporting cable. The descent of the chamber is automatically controlled by a brake cable connected to the chamber and extending from a winch-controlled device fixed to the derrick. The winch-controlled device is similar to a J.R.G. type commercially sold to brake vertical falls. However, the rate of descent of the chamber is again believed to be essentially linear. Moreover, the emergency elevator disclosed within the Bonafos patent may be used in conjunction with a single elevated station of the derrick or other elevated structure.
U.S. Pat. No. 3,880,254 discloses an escape boom for use with an off-shore drilling rig wherein a number of lifelines extend from different points on the rig to the remote head of the escape boom.
U.S Pat. No. 4,050,542 discloses a mobile rescue apparatus for rescuing individuals from a high-rise building. The rescue apparatus includes a telescoping chute, a pair of cable sections extending from the top of the chute to the bottom thereof, and a bag device for supporting the person to be rescued. The rate of descent of the bag device along the chute is controlled by varying the divergence of the pair of cable sections.
In the event of an emergency it is desirable that an escape device permit the initial descent of the endangered person to be relatively rapid in order to remove the endangered person from the site of the emergency. Of course, it is also desirable that the initially rapid rate of descent be decreased as the endangered person approaches the lower end of the escape cable to prevent injury to the endangered person due to impact with the ground at the end of the descent.
As mentioned above, the derrick or other elevated structure may include more than one elevated station from which it may be necessary to escape. For example, a derrick may include an upper station located at the rod basket and a lower station located at the tubing board. It is desirable that the escape device be adapted for use in conjunction with either of such elevated stations.
In view of the foregoing, it is an object of the present invention to provide an escape device which may be used to lower an endangered person from an elevated structure along an escape cable in the event of an emergency wherein the rate of descent of the escape device is automatically controlled to initially permit the endangered person to descend relatively rapidly from the elevated structure while automatically decreasing the rate of descent as the endangered person approaches the lower end of the escape cable.
It is another object of the present invention to provide such an escape device which may be easily adapted for use with two different elevated stations of a derrick or other elevated structure.
It is still another object of the present invention to provide such an escape device which is of relatively simple and compact construction and which may be easily installed upon a derrick, tower, or other elevated structure.
These and other objects of the present invention will become more apparent to those skilled in the art as the description of the present invention proceeds.